(AHMEDABAD, India-AFP) - Indian farmers were urged Thursday to hand over scraps of metal and tools for the world's tallest statue, as construction began on what promoters hope will be a wonder of the world.

The tribute to Sardar Patel, the first home minister of independent India, is set to be twice the size of the Statue of Liberty and four times higher than Christ the Redeemer in Rio de Janeiro.

The metal structure, a pet project of opposition leader Narendra Modi in his home state of Gujarat, will rise 182 metres (600 feet) from an island in the Narmada river when completed in four years' time.

Modi laid the foundation stone on Thursday and urged farmers to donate tools which will be melted down and used in the memorial to a politician nicknamed the "Iron Man of India."

"People come to see the Taj Mahal, flock to America for the Statue of Liberty and France for the Eiffel Tower. Now people from all over the world will come here to see this wonder," Modi said.

"We have asked farmers from every village in India to give old pieces of their agricultural tools, just 200 grams or 400 grams would do," he added from the site at Kevadia, 170 kilometres (105 miles) from Gujarat's biggest city Ahmedabad.

A metal collection effort covering nearly 700,000 villages across the country will begin Thursday and last until January 26 next year, state officials said.

The total cost of the statue is estimated at 25 billion rupees ($300 million) and will be funded with public funds and private donations.

When finished, it will tower by 54 metres over the 128-metre Spring Temple Buddha in China's Henan province which is currently the world's tallest statue.

The memorial has strong political undertones as it honours an independence hero who spent his life in the Congress party, the main rival of Modi's Bharatiya Janata Party (BJP) in national elections next year.

Modi, the BJP's prime ministerial candidate, suggested earlier this week that Patel, who is from Gujarat, would have made a better leader than India's first prime minister Jawaharlal Nehru.

This was a provocative dig at India's modern-day Gandhi political dynasty, led by Congress chief Sonia and her son Rahul, who are descended from Nehru.

The family has ruled for most of India's post-independence history.

The theme of national unity represented by Patel is also attractive to Modi as he tries to paint himself as a secular, centrist candidate in the diverse country of 1.2 billion people.

The Hindu nationalist was chief minister of Gujarat in 2002 when religious riots targeting Muslims left at least 1,000 dead and led to accusations he did too little to stop the violence.

One of his ministers was convicted of instigating the carnage, but he has been cleared of wrongdoing in various official investigations.

Patel was a close friend and ally of Mahatma Gandhi, with whom he shared a prison cell, and became the leader of the Congress Party in 1934.

His lasting legacy was forged in his role as India's first home minister, when he was tasked with moulding a united country from hundreds of semi-autonomous princely states and British-era colonial provinces.

Work on the statue will be undertaken by Turner Construction, the company behind the world's tallest building, the Burj Khalifa in Dubai.